US3630250A

US3630250A - Ammonium nitrate explosive composition

Info

Publication number: US3630250A
Application number: US818087A
Authority: US
Inventors: Joseph R Hradel; Harold E Staadt
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1969-04-21
Filing date: 1969-04-21
Publication date: 1971-12-28
Anticipated expiration: 1988-12-28

Abstract

An explosive composition is provided which contains a distinct particulate ammonium nitrate phase and a distinct aqueous phase saturated with ammonium nitrate.

Description

United States Patent Inventors Joseph R. Hradel Mount Pleasant, Micln;

Harold E. Staadt, Tulsa, Okla.

Apr. 21, 1969 Dec. 28, 1971 The Dow Chemical Company Midland, Mich.

Original application Jan. 5, 1959, Ser. No. 784,881. Divided and this application Apr. 21, 1969, Ser. No. 818,087

Appl. No. Filed Patented Assignee AMMONIUM NITRATE EXPLOSIVE COMPOSITION 13 Claims, No Drawings US. Cl 149/21, 149/40, 149/41, 149/43, 149/44, 149/60, 149/112 Int. Cl C06b l/04 Field of Search 149/21, 40,

References Cited UNITED STATES PATENTS Hradel et al.

Taylor Streng et a1 Cook et a1. Staadt Hradel et a1. Hradel et a1.

Cook et a1. Grifi'lth Primary Examiner-Benjamin R. Padgett Assistant Examiner-Stephen .1, Lechert, Jr.

AllomeysGriswold & Burdick, Bruce M. Kanuch and William R. Norris 149/21 X 149/21 X 149/21 X [49/21 X ABSTRACT: An explosive composition is provided which contains a distinct particulate ammonium nitrate phase and a distinct aqueous phase saturated with ammonium nitrate.

AMMONIUM NITRATE EXPLOSIVE COMPOSITION This is a division of application, Ser. No. 784,88 1 filed Jan. 5, 1959.

it has been a desideratum in the explosives art to formulate and compound explosive compositions which are easily and safely loaded into a borehole or fissure in an earth formation which are of relatively low cost and which do not produce toxic substances on detonation.

Accordingly, it is an object of this invention to provide an ammonium nitrate explosive mixture in the form of an aqueous composition which may be readily loaded as by pumping the composition into a borehole or by first placing the composition, if pasty, in rigid or flexible containers and positioning the containers in a borehole, the aqueous composition having substantially no voids therein and especially when in the form of a slurry the composition further filling any confining space in the manner of a liquid so as to generally eliminate voids below the surface of the slurry.

It is another object of the invention to provide an ammonium nitrate explosive composition which can be prepared from low cost materials.

It is another object of the invention to provide an ammonium nitrate explosive composition compounded from substances which do not produce toxic products when the composition is detonated.

lt is a further object of the invention to provide an ammonium nitrate explosive composition which is readily compounded at or near the site where it is used.

These and other objects are attained upon admixing ammonium nitrate and water in suitable proportions, hereinafter described, whereby there is obtained a paste or slurry of particulated ammonium nitrate in its saturated aqueous solution.

The compositions of the invention may be compounded by first preparing an aqueous solution of ammonium nitrate from water and any grade of ammonium nitrate such as fertilizer grade ammonium nitrate or explosives grade ammonium nitrate, and slurrying therein or mixing therewith a particulated ammonium nitrate. However, a most economical procedure is that of admixing a particulated ammonium nitrate with one of the aqueous ammonium nitrate solutions of commerce such as an aqueous solution containing about 84 percent of ammonium nitrate as obtained in the manufacture of ammonium nitrate.

While a fine particulate grade of ammonium nitrate may be used to obtain a composition with somewhat greater work potential, it is generally more economical to use an inexpensive grade such as fertilizer grade ammonium nitrate in either prilled or granular form and, if necessary, to increase the size of the load slightly. However, though a relatively coarse grade of ammonium nitrate may be employed a grade of ammonium nitrate having more than about 5 percent of particles of a size greater than that passing about a IO'mesh sieve (U.S. Sieve Series) is to be avoided as decreasing the sensitivity of the composition to initiation to an undesirably low level.

The components of the inventions may be combined in pro portions varying from about 75 to 97 percent by weight of ammonium nitrate and from about 3 to 25 percent by weight of water to produce a pasty to pumpable two phase composition, one of the phases being solid ammoniumnitrate, the other an aqueous solution saturated with respect to ammonium nitrate. It is to be understood'that while compositions in this range will under room temperature conditions contain both dissolved ammonium nitrate and solid phase particulate ammonium nitrate, the relative amount of ammonium nitrate in each phase is determined by the temperature of the mixture under equilibrium conditions. At higher temperatures more solid particulate ammonium nitrate will be taken into solution that at lower temperatures.

While such an aqueous composition of ammonium nitrate explosive is detonable upon initiation by a suitably heavy initiator, it is generally to be preferred that the slurry be admixed with up to about 35 percent by weight of a sensitizer to increase sensitivity as well as work potential. In this instance the composition comprises up to 35 percent by weight of a sensitizer, 40-97 percent by weight of ammonium nitrate, a portion of which is in particulate form, and 3-25 percent by weight water containing dissolved ammonium nitrate. Suitable sensitizers include light metals such as magnesium and magnesium-base alloys comprising at least percent of magnesium, and aluminum and aluminum-base alloys comprising at least 80 percent of aluminum, the light metal being in particulated fonn. Atomized pellets of light metal as well as the ground flake form of metal may be used in compounding the explosive composition of the invention. Examples of suitable magnesium-base alloys include those having the ASTM designations ZKlO, ZK60, A241, as well as AZll containing 1 percent of manganese, ZK60 containing 2 percent of thorium, and an alloy containing 2.8 percent of aluminum, 8.4 percent of zinc, the balance magnesium. While the particulated metals may be used in the form of ground or flaked particles a desirable form is that of atomized pellets, for example, atomized metal pellets obtained as described in U.S. Pat. Nos. 2,699,576 and 2,728,107.

Ground metals as produced are generally quite varied in particle size and usually contain a substantial amount of fines passing a 325 mesh sieve. Not only are these fines rather easily ignited in air but they contribute to low level initiation of particulate ammonium nitrate in admixture therewith. Such fines are thus unsuitable in the preparation of relatively insensitive ammonium nitrate explosive mixtures. Ground metals may be used upon separating the fines as by screening and selecting particles about percent of which are retained on a 140 mesh sieve and not more than 1 percent of which pass a 200 mesh sieve. It is also desirable to reject coarse metal particles not passing a 20 mesh sieve as these are too large to react effectively during the brief interval of the detonation reaction of ammonium nitrate, though the presence of a small percent of larger particles does not particularly adversely affect detonability of an ammonium nitrate explosive mixture.

On the other hand atomized metal pellets produced according to the U.S. patents referred to above are readily formed in a narrow range of particle sizes with little fines. While the same limits of metal particle sizes generally apply whether the metal is ground or pelletized the following is a sieve analysis of a suitable pelletized magnesium-base alloy having the ASTM designation ZK60.

Other suitable sensitizers for the present explosive composition include finely divided carbon, preferably passing a 325 mesh sieve, and mixtures of carbon and the above-mentioned particulate light metals. It is to be preferred that the carbonparticulate metal mixtures contain at least 50 to 75 percent by weight of the particulate metal.

Additional sensitizers which may be used include such inorganic salts as potassium nitrate, sodium nitroprusside, potassium ferrocyanide, ammonium chromate, potassium nitrite, strontium nitrate, sodium cyanide, calcium nitrate and-ammonium hypophosphite all of which contain nitrogen and exhibit a melting point or decomposition point above a temperature of C. These inorganic sensitizers are best employed in' the explosive composition of the invention in the range of about l5 to 35 percent by weight of the total composition.

If desired the explosive composition of the invention may be thickened upon admixing therewith from about 0.1 to 5 petcent based on the weight of the liquid phase. of a thickening agent such as methyl cellulose or gum karaya. Other suitable thickening agents are carboxymethyl cellulose, kava kava gum, guar gum, accroides gum, locust bean gum, balsam tolu form of atomized pellets. The particle size of the particulated aluminum was such that about 0.4 percent was retained on a 40 mesh sieve. about 85 percent was retained on 200 mesh sieve and about 0.9 percent passed a 325 mesh sieve.

natural, lrish moss, Iceland moss and high molecular weight 5 The prepared mixtures were loaded into individual shallow polyacrylarnide. boreholes drilled in clay soil and having a diameter of 4 inches Compositions of the invention containing from about 3 w and a depth of about 4 feet. Successive boreholes were spaced 12 percent of water are generally possessed of a pastelike con- 9 20 feet p r The loading of each hole was accomsistency and are more conveniently loaded into accessible Phshad y first P g an "humor the form of a shaped b h l charge armed with a blasting cap in the bottom of the hole and Compositions of the invention containing from about l2 to i the lead Wires of the blasting Cap to firing 90mm] 25 percent ofwater are generally pumpable as a slurry and are switch. Each shaped charge was used and posltroned w1th the useful in loading inaccessible or horizontal or upwardly slop- Jet end ans facing "P q Y- ing borehoes' I The explosrve m xtures contained 1n the plastic bags 1n In preparing and dewnafing the composition of the New which they were mixed were placed in respective testholes, the bag in each case deforming so as to cover the mrtrator. tron, the ingredients of the composition are m1xed together in Sand was used as a tamp, the hole being filled from the bag to small quantities as by kneadmg in a plast1c bag or in larger ground level with sand. Detonation of the mixture was atquantrtres as wrth a mechamcal agitator or paddle mixer. A

tempted by closrng the firing switch thus setting off the initiaload or charge of the so-prepared mixture is placed in the tor at the bottom of the hole. In a comparison test 1n the form desired location, usually 1n the confinement of a borehole. A 8 char 6 Such as a [former containin a char 6 of of a blank, one hole was loaded solely with :1 l0 pound quantil m l J t Pi l t 5 th ty of fertilizer grade of ammonium nitrate and an initiator.

l d q z i l 'g g h e The magnitudes of the detonations obtained were deteranneN i ap mined by measuring the size of the crater produced. While the i ecmc m astmg P s aped a crater size alone is not indication of the amount of earth for- F'f resin to e exploswe lo 1 i mation that is broken up or loosened, it does give an indicamus f meted toward the f y f The tion of the work potential of the mixture detonated. The crater elecmcal lead from blasting cap ngged w a 9" size herein reported shows how much material was thrown suff f mechan'sm to a remote comm! ficiently so as not to fall back over the test hole. Test condil a sand 9' 813W] p p h over the load tions and results are summarized in the table 2. f lhmawf- The load 15 fired "P semhg 03' the blast In order to compare the composition of the invention with .i s e h 8 A conventional explosives varied amounts of 60 percent The h p f f Invention P pared and d nat d dynamite each with a No. 8 Electric Blasting Cap therefor as described is especrally advantageously used in nunmg were placed in shallow test holes 4 feet deep, tamped with operations m which the use of low cost compositions combinsand and detonated. Five pounds of dynamite so loaded and ing the properties of good heave or work potential with lower detonated produced a crater 5 feet in diameter and 1.5 feet range bnsance and low toxicity istobedesired. deep; 10 pounds of dynamite produced a crater 8 feet in To demonstrate the properties of the ammonium explosive diameter and 1 foot deep; while 25 pounds of dynamite mixture of the invention, various embodiments of the invenproduced a crater ll feet in diameter and 5 feet deep. The tion were prepared and tested. In each test a ID or a 25 pound results of the blank, Test No. 15, show the ammonium nitrate quantity of explosive mixture was formulated of a particulated alone is not detonable under these conditions.

TABLE 2 Indicator Composltion Wel ht of Blasting Wt. ol RDX ln Crater dlmenslons. ft. FOAN. Hi0, Al. loa lbs. cap No. shaped charge, percent percent percent 02. Diameter Depth Test N0 10 s 3125 3.. B5 7.5 1.5 10 s 3.25 6 4.5 4... 1o 15 15 10 s 3.25 6 s 5.. so 10 1o 10 s 3.25 5 1. 5 a... 15 a0 10 s 3.25 s a 7... so 25 15 10 s 3.25 s 4 a... s7 3 10 15 s 1 12 3 1;... s5 5 10 25 s 1 12 3 10. so 10 10 25 s 1 12 3 11... 9o 5 5 10 s 3. 25 10 4 12... 75 5 20 10 s 3.25 10 6 1a... 70 a 21 10 s 3. 25 10 5 14... so 5 35 10 s s. 25 10 o 15 100 10 s 1.15

I Heaved and cracked. 3 it. 1 Temp only.

NOTE.-FGAN =fertlllzer grade of ammonium nitrate; RDX =trlmethylene trlnitramlne.

fertilizer grade ammonium nitrate and water, with or without particulated aluminum metal, in the proportions and amounts shown in the table. The individual proportions were in each case mixed in a separate polyethylene plastic bag of sufficient size to readily hold the quantity prepared. The various components of the mixture were weighed into the bag, the bag closed and the contents mixed together by kneading the bag with the hands. The fertilizer grade ammonium nitrate contained about 0.7 percent of wax, 1 percent of diatomaceous earth and 0.3 percent of chalk. The particle size of the ammonium nitrate was such that 94 percent by weight of the particles passed a 20 mesh sieve and 85 percent by weight were retained on a 100 mesh sieve. The aluminum metal was in the In an additional test an explosive load weighing about 4 pounds and having the composition 50 percent of ammonium nitrate, 20 percent of water, and 30 percent of particulated aluminum was used to fill a 3 inch by 12 inch steel pipe nipple which was capped on both ends and laid on the ground. The

I. An explosive composition comprising a particulate ammonium nitrate phase in admixture with an aqueous solution phase saturated with respect to ammonium nitrate, particulate metal sensitizer and a thickening agent for the aqueous solution phase.

2. The composition of claim 1 wherein the thickening agent comprises from about 0.1 to about 5 percent by weight of the composition based on the weight of the aqueous phase.

3. The composition of claim 1 wherein water comprises from about 3 to about 25 percent by weight of the composition.

4. The composition of claim 1 including in addition at least one additional inorganic salt containing nitrogen.

5. The composition of claim 1 including in addition at least one inorganic salt selected from the group consisting of potassium nitrate, sodium nitroprusside, potassium ferrocyanide, ammonium chlorate, potassium nitrate, strontium nitrate, sodium cyanide, calcium nitrate, or ammonium hypophosphite.

6. The composition of claim 1 including in addition an inorganic sensitizer.

7. The composition of claim 1 wherein the particulate metal sensitizer is a light metal.

8. The composition of claim 7 wherein the particulate metal sensitizer comprises up to about 35 percent by weight of the composition.

9. The composition of claim 1 wherein the particulate metal comprises a light metal selected from the group consisting of magnesium, magnesium base alloy, aluminum, aluminum base alloy or mixtures thereof.

10. The composition of claim 1 wherein the thickening agent comprises at least one compound selected from the group consisting of methyl cellulose, gum karaya, carboxymethyl cellulose, kava kava gum, guar gum, accroides gum, locust bean gum, balsam tolu natural, Irish moss, Iceland moss, or high molecular weight polyacrylamide.

11. The composition of claim 1 wherein not more than about 5 percent by weight of the particulate ammonium nitrate are of a size greater than that passing a 10 mesh sieve.

12. An explosive composition comprising from about 40 to abut 97 percent by weight of a particulate ammonium nitrate phase, from about 3 to about 25 percent by weight of an aqueous solution phase saturated with respect to ammonium nitrate, from 0-35 percent of particulate metal sensitizer and from about 0.1 to about 5.0 percent by weight based on the amount of water, of a thickening agent dispersed therein.

13. The composition as defined in claim 11 containing at least one additional inorganic salt containing nitrogen and having whichever is the lowest of the melting point and decomposition point above about 100 C.

Claims

2. The composition of claim 1 wherein the thickening agent comprises from about 0.1 to about 5 percent by weight of the composition based on the weight of the aqueous phase.
3. The composition of claim 1 wherein water comprises from about 3 to about 25 percent by weight of the composition.
4. The composition of claim 1 including in addition at least one additional inorganic salt containing nitrogen.
5. The composition of claim 1 including in addition at least one inorganic salt selected from the group consisting of potassium nitrate, sodium nitroprusside, potassium ferrocyanide, ammonium chlorate, potassium nitrate, strontium nitrate, sodium cyanide, calcium nitrate, or ammonium hypophosphite.
6. The composition of claim 1 including in addition an inorganic sensitizer.
7. The composition of claim 1 wherein the particulate metal sensitizer is a light metal.
8. The composition of claim 7 wherein the particulate metal sensitizer comprises up to about 35 percent by weight of the composition.
9. The composition of claim 1 wherein the particulate metal comprises a light metal selected from the group consisting of magnesium, magnesium base alloy, aluminum, aluminum base alloy or mixtures thereof.
10. The composition of claim 1 wherein the thickening agent comprises at least one compound selected from the group consisting of methyl cellulose, gum karaya, carboxymethyl cellulose, kava kava gum, guar gum, accroides gum, locust bean gum, balsam tolu natural, Irish moss, Iceland moss, or high molecular weight polyacrylamide.
11. The composition of claim 1 wherein not more than about 5 percent by weight of the particulate ammonium nitrate are of a size greater than that passing a 10 mesh sieve.
12. An explosive composition comprising from about 40 to abut 97 percent by weight of a particulate ammonium nitrate phase, from about 3 to about 25 percent by weight of an aqueous solution phase saturated with respect to ammonium nitrate, from 0-35 percent of particulate metal sensitizer and from about 0.1 to about 5.0 percent by weight based on the amount of water, of a thickening agent dispersed therein.
13. The composition as defined in claim 11 containing at least one additional inorganic salt containing nitrogen and having whichever is the lowest of the melting point and decomposition point above about 100* C.